This invention concerns detergent compositions comprising mixtures of orthophosphate and pyrophosphate builder salts and low levels of glassy phosphates.
The use of glassy phosphates with other phosphate builders in detergent compositions is known in the art. For example, mechanical dishwashing compositions incorporating sodium hexametaphosphate are disclosed in U.S. Pat. No. 3,579,455 to Phillip M. Sabatelli et al, issued May 18, 1971. Detergent compositions incorporating glassy phosphates are also disclosed in U.S. Pat. No. 2,568,110 to Irving Beiley et al., issued Sept. 18, 1951. Glassy phosphates have also been known for years as adjuvants in soap and detergent compositions. They are described in U.S. Pat. No. 1,956,515 to Ralph E. Hall, April, 1934, (herein incorporated by reference) and U.S. Pat. No. 2,568,110 to Irving Beiley et al., Sept. 18, 1951, (herein incorporated by reference) and in General and Inorganic Chemistry, J. R. Partington, 4th Edition, MacMillan, 1967, (herein incorporated by reference). However, the prior art does not appear to have recognized the benefit attainable by the use of small amounts of glassy phosphates in conjunction with levels of conventional phosphate builders that are insufficient to provide optimum detergency at the levels of mineral hardness ion encountered in a typical U.S. laundering operation.
Detergency is a complex phenomenon believed to involve very many factors such as cleaning ability, i.e., the ability to remove soil from fabric; and whiteness maintenance, i.e., the ability of the detergent solution to prevent suspended soil from depositing on the fabric. In built detergent systems builders are thought to be beneficial influences on factors such as stabilization of suspended solid soils, emulsification of soils, the surface activity of the aqueous detergent solution, the solubilization of water-insoluble materials, the foam or suds-producing characteristics of the washing solution, peptization of soil agglomerates, neutralization of acid soils, and the like, in addition to the sequestration of mineral constituents present in the washing solution. The action of different builders varies, and no general basis has been found either in physical properties or in chemical structure upon which one can predict in advance the excellence, ranking, or performance of chemical materials or mixtures thereof as detergency builders.
Various inorganic salts such as alkali metal carbonates, bicarbonates, borates, phosphates, and silicates are known to display builder effects. The best of the inorganic builders are the water-soluble polyphosphates and in particular the water-soluble pyrophosphates and tripolyphosphates. Of these, sodium tripolyphosphate (STP) is the builder most generally used in solid detergent compositions. However, STP reverts or hydrolyzes during the crutching and spray-drying processing steps of making detergent products, forming some pyrophosphate and some orthophosphate, the latter being a less efficient builder and having among other disadvantages a detrimental effect on the softness of the fabrics being washed. In fully built solid detergent compositions, the hydrolysis of some of the STP is compensated for by raising the level of STP in the product. There has, however, been a recent tendency for phosphate builders to be reduced or eliminated from detergent compositions because of the ability of these materials to act as a nutrient in promoting the undesirable growth of algae in rivers and lakes. Moreover, a significant drawback in the elimination or reduction of tripolyphosphate builders from detergent products is, as alluded to above, a corresponding decrease in whiteness maintenance.
Water-soluble pyrophosphates are also effective detergent builders when utilized alone or with the tripolyphosphates. Pyrophosphate products in which no tripolyphosphate is present contain small levels of orthophosphates, which are present as impurities in the pyrophosphate as obtained from the supplier. Pure pyrophosphate products ordinarily contain from about 0.5% to 5% of orthophosphate by weight of the pyrophosphate. "Pure" pyrophosphate products indicate that the product formulation is intended to contain pyrophosphate as the only phosphate species, but which on a commercial scale contain other species of phosphates. The "pure" pyrophosphate built products are particularly sensitive to whiteness maintenance problems because of the lack of tripolyphosphates which provide a slight whiteness maintenance benefit.
Particulate soil redeposition is most evident in laundry wash solutions containing phosphate builders when the molar ratio of builder to mineral hardness ion is in a range that is slightly less than 1:1. The redeposition is particularly severe when mixtures of pyrophosphates and orthophosphate are present, such mixtures commonly occurring as a result of the reversion of sodium tripolyphosphate during crutching and spray drying of detergent compositions. This particular redeposition problem is referred to hereinafter as the "pyro-dip" because of the decrease in whiteness maintenance performance that is observed if fabric laundering is carried out under these conditions.
It has also been observed that detergent compositions formulated in accordance with the present invention enjoy the added benefit due to the incorporation of the glassy phosphate of reducing deposition not only upon the fabrics but also of the builder salts and surfactants upon exposed machine surfaces. For instance, it has been observed in sodium tripolyphosphate products which contain substantial amounts of reverted pyrophosphate and orthophosphate, that deposition upon the machine surfaces can be a significant problem. This is most often discovered by the consumer when the washing machine drum is removed for repair. While there is no buildup on the inner surface of the tub where the fabrics are constantly abrading, the buildup on the outer surface of the washing machine drum of surfactant and phosphate salts can be severe. In particular, the salts of organic sulfuric and sulfonic acids (surfactants, have been observed as deposits on washing machine surfaces.
Accordingly, a primary object of the invention is the attainment of satisfactory detergency performance with compositions in which the level of phosphate builders is less than that necessary to sequester all of the mineral hardness present under normal usage conditions.
A further object of the invention is the provision of an optimum builder mixture having detergency building properties substantially greater than the additive contributions of the components thereof.
A further object of the present invention is to provide for phosphate built detergent compositions in which insoluble surfactant and insoluble phosphate salt buildup upon machine surfaces is reduced.
It is also an object of the invention to provide detergent compositions which are effective in water solutions over a wide range of concentrations inasmuch as the conditions under which household laundry is washed vary quite widely with the individual. Throughout the specification and claims, percentages and ratios are by weight and temperatures in degrees Fahrenheit unless otherwise indicated.